László Hegedüs

Nonlinear effects of electrolyte diodes and transistors in a polymer gel medium

The polarization curve of an acid-base interface in a hydrogel medium has a diode characteristic. Two of each such electrolyte diodes can be combined to give an electrolyte transistor. When a salt is added to the alkaline or to the acidic part of a reverse biased electrolyte diode, the current response is highly nonlinear. If the salt is added to the acidic side, even bistability can be observed. This bistability can generate complex oscillations in a base-acid-base electrolyte transistor. These nonlinear effects are studied experimentally and theoretically. While the nonlinear salt effect can be explained with the Nernst-Planck equations, to understand the bistable behavior further investigations are necessary. (c) 1999 American Institute of Physics.

Hydrogenation of pyrrole derivatives: Part V. Poisoning effect of nitrogen on precious metal on carbon catalysts

Poisoning of different precious metals on carbon catalysts (Pd/C, Ru/C and Rh/C) was observed in the hydrogenation of some pyrrole derivatives, under mild reaction conditions, in non-acidic medium. In all reductions, the catalysts were poisoned by the hydrogenated products (pyrrolidines) more strongly than by the reactants (pyrroles). A comparison concerning poison sensitivity of the catalytic metals was also made.

Hydrogenation of pyrrole derivatives. II. Hydrogenations over supported noble metal catalysts

Abstract The heterogeneous catalytic hydrogenation of 1-methyl-2-pyrroleethanol resulted in 1-methyl-2-pyrrolidineethanol, an important and valuable pharmaceutical intermediate. Various noble metal catalysts on different supports have been screened. The best results were achieved with a carbon supported rhodium catalyst, in non-acidic medium, under mild reaction conditions (6 bar, room temperature). Ruthenium on carbon also showed high activity in this hydrogenation.

Hydrogenation of pyrrole derivatives. Part IV. Hydrogenation of 1-methylpyrrole

Abstract The heterogeneous catalytic hydrogenation of 1-methylpyrrole was investigated in non-acidic medium. Various supported noble metal catalysts and solvents have been screened. The highest activities were provided by rhodium and ruthenium catalysts. In palladium mediated hydrogenations the activity of the catalyst was increased by appropriate solvents. The reactivity of 1-methylpyrrole was compared with that of pyrrole and its derivatives hydrogenated previously.

Chemical mechanism of the radical feedback loop in the classical BZ reaction. Malonyl bromite and oxalic acid as flow-through intermediates

High-pressure liquid chromatography (HPLC) and measurements of the CO2 produced were performed in the induction period of the classical Belousov–Zhabotinsky (BZ) reaction (malonic acid–bromate–cerium catalyst in sulfuric acid medium). It was found that oxalic acid is a flow-through intermediate of the reaction. This was confirmed with an independent qualitative test with thiobarbituric acid. The concentration of oxalic acid grows in the induction period together with that of bromomalonic acid and dibromomalonic acid intermediates. It is known that there are two negative feedback loops in the BZ reaction: one is ia bromide and the other ia organic free radicals. Oxalic acid and also CO2 are products of this second loop where organic radicals react with BrO2 radicals. The induction period was chosen for the present experimental studies because the above radical–radical reactions are most intense during that time. Based on the experimental results mechanistic proposals are made for the radical feedback loop. A method to accumulate multivalent organic acids present in very low concentrations in the BZ reaction was also developed. Applying this and a thermal decomposition method ethenetetracarboxylic acid (EETA) was identified as an oxidation product of ethanetetracarboxylic acid (ETA).

Monodechlorination of6,6-Dichloro-3-phosphabicyclo[3.1.0]hexane 3-Oxides by CatalyticHydrogenation†

Catalytic hydrogenation of the title compounds atca. 88 °C and 9 bar in the presence of diethylamineled to a reasonable portion of monochlorocyclopropanes togetherwith ca. 38% of hexahydrophosphinine oxides.